This invention relates to electronic control devices for controlling the output current of the alternator (AC generator of the automobile) in response to the state of the electric load, thereby realizing a stable control of the idling rpm of the engine.
The conventional automotive electronic control device, disclosed, for example, in Japanese Laid-Open Patent (Kokai) No. 1-247238, predicts the output current level of the alternator from the field duty signal (the control signal of the alternator, i.e., the on/off signal for the current supply to the field coil of the alternator), and performs the duty control in such a manner that when the duty factor of the signal increases, the current supplied to the field coil is forcibly turned off to reduce the duty factor to zero percent. The duty factor is increased gradually thereafter.
The above conventional electronic control device, however, has the following disadvantage. An accurate detection of the duty factor of the field duty signal requires an averaging thereof over a predetermined length of interval. Thus the detection of the duty factor immediately after the electric load is made tends to be late. It is thus impossible to prevent the substantial reduction of the idling rpm of the engine immediately after the making of the electric load. Further disadvantage is that since the output current is predicted on the basis of the field duty signal, the prediction error increases when the resistance of the field coil changes due to the variation of the ambient temperature. The accuracy and the reliability of control is then reduced.